Objective: The current study aims to investigate the effect of a) caloric restriction (very low calorie diet (VLCD)); b) caloric restriction with mechanical restriction (Laparoscopic adjustable gastric banding (LAGB)); and c) caloric restriction with mechanical restriction and physiological changes through malapsorption (Roux- en- Y bypass (RYGB) surgery) on gut-brain interactions to find an optimal balance for weight loss and long-term sustained weight maintenance.